perlstyle

NAME

DESCRIPTION

Each programmer will, of course, have his or her own preferences in
regards to formatting, but there are some general guidelines that will
make your programs easier to read, understand, and maintain.

The most important thing is to run your programs under the -w
flag at all times. You may turn it off explicitly for particular
portions of code via the nowarnings
pragma or the $^W
variable
if you must. You should also always run under usestrict
or know the
reason why not. The usesigtrap
and even usediagnostics
pragmas
may also prove useful.

Regarding aesthetics of code lay out, about the only thing Larry
cares strongly about is that the closing curly bracket of
a multi-line BLOCK should line up with the keyword that started the construct.
Beyond that, he has other preferences that aren't so strong:

4-column indent.

Opening curly on same line as keyword, if possible, otherwise line up.

Space before the opening curly of a multi-line BLOCK.

One-line BLOCK may be put on one line, including curlies.

No space before the semicolon.

Semicolon omitted in "short" one-line BLOCK.

Space around most operators.

Space around a "complex" subscript (inside brackets).

Blank lines between chunks that do different things.

Uncuddled elses.

No space between function name and its opening parenthesis.

Space after each comma.

Long lines broken after an operator (except and
and or
).

Space after last parenthesis matching on current line.

Line up corresponding items vertically.

Omit redundant punctuation as long as clarity doesn't suffer.

Larry has his reasons for each of these things, but he doesn't claim that
everyone else's mind works the same as his does.

Here are some other more substantive style issues to think about:

Just because you CAN do something a particular way doesn't mean that
you SHOULD do it that way. Perl is designed to give you several
ways to do anything, so consider picking the most readable one. For
instance

Similarly, just because an operator lets you assume default arguments
doesn't mean that you have to make use of the defaults. The defaults
are there for lazy systems programmers writing one-shot programs. If
you want your program to be readable, consider supplying the argument.

Along the same lines, just because you CAN omit parentheses in many
places doesn't mean that you ought to:

Don't be afraid to use loop labels--they're there to enhance
readability as well as to allow multilevel loop breaks. See the
previous example.

Avoid using grep() (or map()) or `backticks` in a void context, that is,
when you just throw away their return values. Those functions all
have return values, so use them. Otherwise use a foreach()
loop or
the system() function instead.

For portability, when using features that may not be implemented on
every machine, test the construct in an eval to see if it fails. If
you know what version or patchlevel a particular feature was
implemented, you can test $]
($PERL_VERSION
in English
) to see if it
will be there. The Config
module will also let you interrogate values
determined by the Configure program when Perl was installed.

While short identifiers like $gotit
are probably ok, use underscores to
separate words in longer identifiers. It is generally easier to read
$var_names_like_this
than $VarNamesLikeThis
, especially for
non-native speakers of English. It's also a simple rule that works
consistently with VAR_NAMES_LIKE_THIS
.

Package names are sometimes an exception to this rule. Perl informally
reserves lowercase module names for "pragma" modules like integer
and
strict
. Other modules should begin with a capital letter and use mixed
case, but probably without underscores due to limitations in primitive
file systems' representations of module names as files that must fit into a
few sparse bytes.

You may find it helpful to use letter case to indicate the scope
or nature of a variable. For example:

$ALL_CAPS_HERE constants only (beware clashes with perl vars!)

$Some_Caps_Here package-wide global/static

$no_caps_here function scope my() or local() variables

Function and method names seem to work best as all lowercase.
E.g., $obj->as_string()
.

You can use a leading underscore to indicate that a variable or
function should not be used outside the package that defined it.

If you have a really hairy regular expression, use the /x modifier and
put in some whitespace to make it look a little less like line noise.
Don't use slash as a delimiter when your regexp has slashes or backslashes.

Use the new and
and or
operators to avoid having to parenthesize
list operators so much, and to reduce the incidence of punctuation
operators like && and ||. Call your subroutines as if they were
functions or list operators to avoid excessive ampersands and parentheses.

Always check the return codes of system calls. Good error messages should
go to STDERR
, include which program caused the problem, what the failed
system call and arguments were, and (VERY IMPORTANT) should contain the
standard system error message for what went wrong. Here's a simple but
sufficient example:

Think about reusability. Why waste brainpower on a one-shot when you
might want to do something like it again? Consider generalizing your
code. Consider writing a module or object class. Consider making your
code run cleanly with usestrict
and usewarnings
(or -w) in
effect. Consider giving away your code. Consider changing your whole
world view. Consider... oh, never mind.

Try to document your code and use Pod formatting in a consistent way. Here
are commonly expected conventions:

use C<>
for function, variable and module names (and more
generally anything that can be considered part of code, like filehandles
or specific values). Note that function names are considered more readable
with parentheses after their name, that is function()
.

use B<>
for commands names like cat or grep.

use F<>
or C<>
for file names. F<>
should
be the only Pod code for file names, but as most Pod formatters render it
as italic, Unix and Windows paths with their slashes and backslashes may
be less readable, and better rendered with C<>
.